The present invention relates to an installation structure of a length meter under vacuum for measuring the displacement of an object to be measured, which is placed in vacuum, using a length meter including an optical interferometer.
In general, an electron scanning microscope or a semiconductor inspection apparatus includes mechanisms systems having an electronic optical system which generates an enlarged image of a specimen using electron beams, an electron beam detector which captures an electron image to be stored in the apparatus, an image processing engine which detects defects and the like of the specimen from the stored image, an XY stage which moves the specimen while transporting or positioning the specimen at high accuracy, and the like, and is configured to irradiate the specimen with electron beams while moving or tilting the specimen in an arbitrary direction using the XY stage in a state where the specimen is adsorbed and fixed onto the XY stage, detect secondary electrons or backscattered electrons generated from the specimen, and obtain a scanned image of the specimen.
As a unit for measuring an accurate displacement amount of the specimen moved by the XY stage, a laser length meter is used. In an apparatus which requires a sub-nm or μm resolution or smaller, the length meter is also installed in a vacuum chamber together with the XY stage that supports the specimen (for example, refer to patent references 1 and 2).
FIG. 10 illustrates an installation mode of a length meter in an apparatus according to the related art. As illustrated in FIG. 10, the length meter 1 is stored in a vacuum chamber A together with an XY stage 3 supported by a stage mount 2, and the displacement of a specimen (not illustrated) suctioned and fixed onto a corresponding stage is detected by measuring the displacement of the XY stage 3 using the length meter 1.
Specifically, by a driving mechanism (not illustrated) which is installed on the stage mount 2 supported by a surface plate (not illustrated) and includes rails in both X and Y directions, a driving shaft, a driving motor, and the like, the XY stage 3 is provided to be moved flexibly in each of the directions, and is provided to suction and fix the specimen transported by a transporting mechanism (not illustrated) stored in the same vacuum chamber A, to a predetermined position on the upper surface. At one corner of four corners of the XY stage 3, stage mirrors 4 are mounted along both side portions with the corner interposed therebetween.
In addition, the length meter 1 is mounted on an installation base 5 installed on a side of the XY stage 3, and is provided so that laser light for measurement is input from an optical axis adjuster 6 provided on the outside of a side wall A1 of the vacuum chamber A to the rear surface of the length meter 1, the laser light is output from the front surface of the length meter 1 toward the stage mirror 4, the laser light that is incident on the stage mirror 4 and is reflected therefrom is received by the front surface of the length meter 1, and interference light in the length meter 1 is output to a pick-up unit 7 disposed on the outside of the side wall A1 of the vacuum chamber A.
In addition, a detection signal input to the pick-up unit 7 is input to a length measurement calculator (not illustrated) to measure the displacement amount of the specimen moved along with the XY stage 3.
The illustrated length meter 1 has a configuration in which the front surface is provided as an input surface of the laser light directed toward the stage mirror 4 which is an object to be measured and the rear surface is provided as an output surface of the detection laser light directed toward the pick-up unit 7. However, unlike this, when a length meter 1 having a configuration in which the input surface and the output surface of the laser light are arranged in a perpendicular direction is used, as illustrated in FIG. 11, the optical axis adjuster 6 and the pick-up unit 7 are disposed on the outside of the side wall A1 of the vacuum chamber A which opposes the side wall of the length meter 1.    [Patent Reference 1] Japanese Patent Application Laid-open No. 2003-282423.    [Patent Reference 2] Japanese Patent Application Laid-open No. 2005-327917.